As a power supply circuit, a direct current (DC)-DC converter that performs conversion of DC voltage is known. For example, in an information processing device such as a server and a home appliance, alternating current (AC) voltage is converted into DC voltage using a rectifier and a power factor correction circuit. After the conversion, the DC voltage is stepped down using the DC-DC converter.
As a control method of a power supply circuit, a method of performing pulse width modulation (PWM) control on a switching element is known. In the PWM control, a pulse width of a PWM signal is modulated by comparing a carrier signal and a reference signal. The reference signal is generated on the basis of output voltage of a power supply circuit.
The switching element is turned on and off in response to the PWM signal that is modulated as described above. It is known that a switching frequency is controlled depending on the load in order to improve efficiency of the power supply circuit.
A method of changing a switching frequency by changing amplitude of a carrier signal is known (for example, first and second embodiments in Japanese Laid-open Patent Publication No. 2009-100607). In addition, it is known that a switching frequency is controlled by changing the slope of the wave of the carrier signal (for example, a third embodiment in Japanese Laid-open Patent Publication No. 2009-100607).
When the slope of the carrier signal wave is changed, selection of the frequency is limited because a switching frequency of a high frequency corresponds to an integral multiple of a switching frequency of a low frequency. Furthermore, when the amplitude of the carrier signal is changed, a transient response is undesirably generated in the output voltage of the power supply circuit because a duty ratio of the PWM signal varies at the time of change of the switching frequency.
An object of the control device, the control method, and the power supply device according to the embodiments is to stabilize the output voltage.